As microelectronic packages become more densely populated with highly integrated components, the increasing integration calls for more individual conductors within each package. Signals must be conducted between ever more sophisticated chips that have more contacts to be connected to, but along smaller lengths of the chip beachfront. While the growing sophistication calls for a fatter data pipe between components to match the higher integration, the overall miniaturization, forces the opposite: the numerous conductors (wires, lines, traces) needed to connect dies, chips, and components to each other must become thinner and more numerous per unit area, or per unit length of beachfront of the chips, to keep pace with the miniaturization. These thinner traces result in a leaner and more constricted data path for individual signals, even though the overall data pipe as a whole has more conductors because they are thinner. At higher density, the traces become skinny, with high resistance and very high capacitance, limiting transmission bandwidth.
These thinner conductive lines, more densely packed and confined between smaller dies and chips, introduce some limitations. For example, a package may require that 10,000 conductive lines be packed into the ever-shrinking real estate of a smaller footprint. This high number of skinny, densely packed conductors, must be arrayed at extremely fine pitches. The thinness of the individual conductors and the decreasing amount of dielectric between these finely pitched conductors results in a first-order resistive-capacitive (RC) limitation for transmission of signals across the conductors, especially at higher frequencies. This RC limitation also limits the effective length of these thin and finely pitched conductors, especially when hundreds or thousands of the conductors are layered, ribboned, or bundled to connect high bandwidth dies or chips to each other across even a small distance.
FIG. 1 shows conventional ways to address the limitations introduced above. Conventional rigid and flexible interposers 100, whether made of silicon, glass, polyimide, glass-reinforced epoxy laminate, and other materials, have their drawbacks. Generally, an interposer is a layer or adapter that spreads a connection to a wider pitch or reroutes one connection to a different connection. Conventional interposers are relatively expensive and have a bandwidth limitation. For example, limitations in rate for high bandwidth memory (HBM) dynamic random access memory (DRAM) of 1 gigatransfer per second (GT/s) per pin and global package bandwidth of 128 gigabytes per second (GB/s) is mainly due to the limitations of conventional interposers. Likewise HBM2 is limited to about 2 GT/s per pin and global package bandwidth of 256 GB/s for the same reason. The low speed per trace in conventional interposers also requires that many traces be used. Conventional silicon or glass interposer solutions are limited in the number of routing layers they can contain, and by their inability to conserve space. Glass can be subject to the same limitations due to the resistance and capacitance of the traces in the wafer process. Silicon is similarly impractical.
Embedded multi-die interconnect bridges (EMIBs) 120, such as the EMIBs 120 shown in the flip chip ball grid array (FCBGA) of FIG. 1, are another way to address the bandwidth limitations of skinny conductive lines in highly miniaturized routing layers and conventional interposers. An EMIB 120 can take the form of a bridge between dies, usually disposed in a build-up layer. While less expensive than a full conventional interposer, EMIBs still have a bandwidth limitation near or below 2 GHz due to a large resistive-capacitive (RC) load imposed by limited routing layers.
Conventional organic interposers offer yet another attempt at addressing the bandwidth limitations of highly miniaturized conductors. The conventional organic interposers provide improved transmission bandwidth, sometimes up to 40 GHz and beyond, and have good size capabilities, but when they get large, conventional organic interposers warp, and fine-pitch, high density interconnections to a warped surface are difficult. Conventional organic interposers are also limited to only one or two routing layers situated above the surface of the core layer.